Power semiconductor device and methods for fabricating the same

ABSTRACT

A power semiconductor device includes: a drain region of a first conductive type; a drift region of a first conductive type formed on the drain region; a first body region of a second conductive type formed below an upper surface of the drift region; a second body region of a second conductive type formed below the upper surface of the drift region and in the first body region; a third body region of a second conductive type formed by protruding downwards from a lower end of the first body region; a source region of a first conductive type formed below the upper surface of the drift region and in the first body region; and a gate insulating layer formed on channel regions of the first body region and on the drift region between the first body regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/443,371, filed on Apr. 10, 2012, which claims the benefit of KoreanPatent Application No. 10-2011-0035212, filed on Apr. 15, 2011, in theKorean Intellectual Property Office. The just mentioned disclosures areincorporated herein by reference in their entirety.

BACKGROUND

The inventive concept relates to a power semiconductor device, and moreparticularly, to a power semiconductor device having a low on-resistanceand a high breakdown voltage and a method of fabricating thesemiconductor device.

Power semiconductor devices, for example, metal-oxide semiconductorfield-effect transistors (MOSFETs) or insulation gate bi-polartransistors (IGBTs) for power devices must satisfy characteristics suchas a high breakdown voltage and a low on-resistance.

SUMMARY

The inventive concept provides a power semiconductor device having ahigh breakdown voltage and a low on-resistance.

The inventive concept also provides a method of fabricating a powersemiconductor device having a high breakdown voltage and a lowon-resistance.

According to an aspect of the inventive concept, there is provided apower semiconductor device including: a drain region of a firstconductive type; a drift region of a first conductive type formed on thedrain region; a first body region of a second conductive type formedbelow an upper surface of the drift region; a second body region of asecond conductive type formed below the upper surface of the driftregion and in the first body region, and formed to have a depthshallower than that of the first body region; a third body region of asecond conductive type formed by protruding downwards from a lower endof the first body region; a source region of a first conductive typeformed below the upper surface of the drift region and in the first bodyregion, and formed to have a depth shallower than that of the secondbody region; a gate insulating layer formed on channel regions of thefirst body region and on the drift region between the first bodyregions; a gate electrode formed on the gate insulating layer; a sourceelectrode electrically connected to the source region; and a drainelectrode electrically connected to the drain region.

The first body region may have a doping concentration of the secondconductive type lower than that of the second body region, and the thirdbody region may have a doping concentration of the second conductivetype lower than that of the second body region.

The power semiconductor device may be a metal-oxide semiconductorfield-effect transistor (MOSFET). The first conductive type may be ann-type and the second conductive type may be a p-type or the firstconductive type may be a p-type and the second conductive type may be ann-type.

The first body region may include at least one stripe type region andmay further include frame regions connected to both end sides of thefirst body regions. The gate insulating layer may be formed in a stripetype in the same direction as the first body regions. Edge regions ofthe first body regions may have a radius of curvature greater than 100μm.

The first body regions may include polygonal shape unit cells.

The drain region may have a doping concentration of the first conductivetype higher than that of the drift region, and the source region mayhave a doping concentration of the first conductive type higher thanthat of the drift region.

A width of the drift region that overlaps the gate electrode between thefirst body regions may have a size by which a depletion region formed byextending from the first body region forms a planar junction structure.

The power semiconductor device may further include an additional driftregion of a first conductive type formed below the upper surface of thedrift region, surrounding the first body region and the third bodyregion, wherein the additional drift region has a doping concentrationof the first conductive type higher than that of the drift region.

The third body region may be disposed between the gate electrodesadjacent to each other. The third body region may have a depth deeperthan that of the first body region.

The source region may be formed on a position where it overlaps with aportion of the gate electrode and a portion of the source electrode. Thefirst body region may be formed on a position where it overlaps with aportion of the gate electrode and the source electrode.

According to another aspect of the inventive concept, there is provideda power semiconductor device. The power semiconductor device includes: acollector region of a second conductive type; a drift region of a firstconductive type formed on the collector region; a first base region of asecond conductive type formed below an upper surface of the driftregion; a second base region of a second conductive type formed belowthe upper surface of the drift region and in the first base region andformed shallower than the depth of the first base region; a third baseregion of a second conductive type formed by protruding downwards from alower end of the first base region; an emitter region of a firstconductive type formed below the upper surface of the drift region andin the first base region, and formed to have a depth shallower than thatof the second base region; a gate insulating layer formed on channelregions of the first base regions and on the drift region between thefirst base regions; a gate electrodes formed on the gate insulatinglayer; an emitter electrode electrically connected to the emitterregion; and a collector electrode electrically connected to thecollector region.

The first base region may have a doping concentration of the secondconductive type lower than that of the second base region, and the thirdbase region may have a doping concentration of the second conductivetype lower than that of the second base region.

The power semiconductor device may be an insulation gate bipolartransistor (IGBT).

According to an aspect of the inventive concept, there is provided amethod of fabricating a power semiconductor device.

The method includes: forming a drain region of a first conductive type;forming a drift region of a first conductive type on the drain region;forming a first body region of a second conductive type below an uppersurface of the drift region; forming a second body region of a secondconductive type having a depth shallower than that of the first bodyregion below the upper surface of the drift region and in the first bodyregion; forming a third body region of a second conductive typeprotruded downwards from a lower end of the first body region; forming asource region of a first conductive type having a depth shallower thanthat of the second body region below the upper surface of the driftregion and in the first body region; forming a gate insulating layer onchannel regions of the first body regions and on the drift regionbetween the first body regions; forming a gate electrode on the gateinsulating layer; forming a source electrode electrically connected tothe source region; and forming a drain electrode electrically connectedto the drain region.

The first body region may have a doping concentration of the secondconductive type lower than that of the second body region, and the thirdbody region may have a doping concentration of the second conductivetype lower than that of the first body region.

The forming of the first body region may be performed after performingthe forming of the third body region and the forming of the second bodyregion may be performed after performing the forming of the first bodyregion.

In the power semiconductor device and the method of fabricating thepower semiconductor device according to the inventive concept, abreakdown voltage is increased and an on-resistance is reduced byreducing an edge electric field while minimizing the increase in a JFETresistance.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the inventive concept will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a power semiconductor device, forexample, a metal-oxide semiconductor field-effect transistor (MOSFET),according to an embodiment of the inventive concept;

FIG. 2 is a cross-sectional view showing a doping profile of the powersemiconductor device of FIG. 1, according to an embodiment of theinventive concept;

FIG. 3 is a layout of a portion of a power semiconductor deviceaccording to another embodiment of the inventive concept;

FIG. 4 is a layout showing a frame region and a body region of a powersemiconductor device according to another embodiment of the inventiveconcept;

FIG. 5 is a layout of a power semiconductor device according to anotherembodiment of the inventive concept;

FIG. 6 is a cross-sectional view of a power semiconductor device, forexample, a MOSFET, according to another embodiment of the inventiveconcept;

FIG. 7 is a cross-sectional view of a power semiconductor device, forexample, a MOSFET, according to another embodiment of the inventiveconcept;

FIG. 8 is a cross-sectional view of a power semiconductor device, forexample, an insulation gate bi-polar transistor (IGBT), according toanother embodiment of the inventive concept;

FIG. 9, which consists of FIGS. 9A, 9B, 9C, and 9D, shows simulationresults of doping concentrations with respect to a power semiconductordevice according to an embodiment of the inventive concept;

FIG. 10, which consists of FIGS. 10A, 10B, 10C, and 10D, showssimulation results of field effects generated in a power semiconductordevice according to an embodiment of the inventive concept;

FIG. 11 is a graph showing the magnitude of an electric field along theline A-A′ of FIG. 10;

FIG. 12 is a graph showing a test result of a relationship between abreakdown voltage and a specific resistance R_(sp) of a powersemiconductor device according to an embodiment of the inventiveconcept; and

FIGS. 13 through 16 are cross-sectional views for explaining a method offabricating a power semiconductor device according to an embodiment ofthe inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The inventive concept will be described more fully with reference to theaccompanying drawings, in which exemplary embodiments of the presentinvention are shown.

This invention may, however, be embodied in many different forms andshould not construed as limited to the exemplary embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. In the drawings, lengths andsizes of layers and regions may be exaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on” another element or layer, the element or layer may bedirectly on another element or layer or intervening elements or layers.In contrast, when an element is referred to as being “directly on”another element or layer, there are no intervening elements of layerspresent. Like reference numerals in the drawings denote like elementsthroughout. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third,etc., may be used herein to describe various elements, these elementsshould not be limited by these terms. These terms are only used todistinguish one element from another. Thus, a first element could betermed a second element and a second element could be termed a firstelement without departing from the teachings of the present inventiveconcept.

Spatially relative terms, such as “below” or “lower” and the like, maybe used herein for ease of description to describe the relationship ofone element or feature to another element(s) or feature(s) asillustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation, in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as “below” other elements or features would then beoriented “above” the other elements or features. Thus, the exemplaryterm “below” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptions used interpretedaccordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.The singular forms include the plural forms unless the context clearlyindicates otherwise. It will further understood that the terms“comprise” and/or “comprising” when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

A first conductive type may be an n-type and a second conductive typemay be a p-type, and hereinafter, for convenience of explanation, theseterms are used. However, the technical sprit of the inventive concept isnot limited thereto, for example, the first conductive type may be ap-type and the second conductive type may be an n-type.

First, the variation of a breakdown voltage according to a junctionstructure in a metal-oxide semiconductor field-effect transistor(MOSFET) will be described. An ideal breakdown voltage BV_(pp) of ajunction having an infinite planar structure is determined by Equation 1below.

$\begin{matrix}{{BVpp} = {5.34 \times 10^{13} \times {Na}^{\frac{- 3}{4}}}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

where, N_(a) is a doping concentration of a drift layer.

Accordingly, it may be seen that an ideal breakdown voltage BV_(pp) of ajunction having a planar structure depletion region is only determinedby a doping concentration.

Also, a punch-through type breakdown voltage BV_(pt) may be determinedby Equation 2 below.

$\begin{matrix}{{BVpt} = {4010 \times {Na}^{\frac{1}{8}} \times \frac{{qNaWp}^{2}}{ɛ_{s}}}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

where, W_(p) is a thickness of a drift layer, and ∈_(s) is a dielectricconstant.

Accordingly, because the breakdown voltage BV_(pt) is determinedaccording to the concentration and thickness of a drift layer, thepunch-through type breakdown voltage BV_(pt) may vary according to thetype of a junction structure.

Next, a breakdown voltage BV_(sp) of a junction having a spherical typedepletion region is described. When a high voltage is applied to a powerMOSFET having a polygonal structure unit cell, an extended depletionregion has a spherical shape. Because an electric field is concentratedon a region having the smallest radius of curvature, the breakdownvoltage BV_(sp) varies according to not only the characteristics of araw material but also a junction depth. The breakdown voltage BV_(sp) ofa spherical type structure is practically determined by Equation 3below.

$\begin{matrix}{{BVsp} = {{BVpp} \times \{ {\frac{{rj}^{2}}{Wc} + {2.14 \times \frac{{rj}^{\frac{6}{7}}}{Wc}} - ( {\frac{{rj}^{3}}{Wc} + {3 \times \frac{{rj}^{\frac{13}{7}}}{Wc}}} )^{\frac{2}{3}}} \}}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

where, r_(j) is a junction depth and W_(c) is a critical depletiondepth.

Accordingly, it may be seen that a breakdown voltage BVs_(p) in aspherical type structure is much lower than the ideal breakdown voltageBV_(pp).

Next, a breakdown voltage of a junction having a cylindrical typedepletion region is described. In a case when a unit cell has a linearstructure, a body region on which the unit cell is formed also has alinear structure. At this point, if a distance between the adjacent bodyregions is remote, the depletion region expands in a cylindrical shape.The breakdown voltage BV_(cyl) of a cylindrical type structure isdetermined by Equation 4 below.

$\begin{matrix}{{BVcyl} = {{BVpp} \times \{ {{\frac{1}{2} \times ( {\frac{{rj}^{2}}{Wc} + {2 \times \frac{{rj}^{\frac{6}{7}}}{Wc}}} ) \times {{Ln}( {1 + {2 \times \frac{{Wc}^{\frac{8}{7}}}{rj}}} )}} - \frac{{rj}^{\frac{6}{7}}}{Wc}} \}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

Referring to Equations 1 through 4, it may be seen that the breakdownvoltage BV_(cyl) of the cylindrical type structure is higher than thebreakdown voltage BVs_(p) of the spherical type structure, but is lowerthan the ideal breakdown voltage BV_(pp). This denotes that when ajunction in a device has a depletion region having a spherical shapestructure and a cylindrical shape structure, the junction of the devicemay have a breakdown voltage much lower than the ideal breakdown voltageBV_(pp) with respect to a planar structure depletion region. In order tocompensate for the reduced breakdown voltage due to the structuralcause, the increases in the specific resistance and thickness of thedrift layer are required. However, if the specific resistance andthickness of the drift layer are increased, an on-resistance isincreased.

FIG. 1 is a cross-sectional view of a power semiconductor device, forexample, a MOSFET, according to an embodiment of the inventive concept.

Referring to FIG. 1, a drift region 104 of a first conductive type maybe formed on a drain region 102 of a first conductive type, wherein thedrain region 102 may be a semiconductor substrate. The concentration ofimpurities in the drift region 104 may be reduced from top to down. Thedrift region 104 may have a concentration of the first conductive typelower than that of the drain region 102.

A first body region 106 of a second conductive type may be formed on anupper predetermined region of the drift region 104. That is, the firstbody region 106 may be formed below an upper surface of the drift region104. The first body region 106 may be formed on a position where itoverlaps with a portion of a gate electrode 118 and a source electrode120.

A second body region 107 of a second conductive type may be formed belowthe upper surface of the drift region 104 and in the first body region106. The first body region 106 has a doping concentration lower thanthat of the second body region 107. The second body region 107 has adepth shallower than that of the first body region 106. That is, thefirst body region 106 has a lowest end deeper than that of the secondbody region 107. In the current inventive concept, “is formed deeper”denotes that a distance from the upper surface of the drift region 104,on which the gate electrodes 118 are formed, towards the drain region102 is farther in a vertically downwards direction.

A third body region 109 of a second conductive type may be formed on alower end of the first body region 106 by protruding downwards. Asexemplary, the third body region 109 may protrude downwards from acentral portion of the first body region 106; however, the inventiveconcept is not limited to the central portion. The third body, region109 has a concentration of the second conductive type lower than that ofthe second body region 107. The third body region 109 and the first bodyregion 106 may have the same concentration of the second conductivetype. Alternatively, the third body region 109 may have a concentrationof the second conductive type higher or lower than that of the firstbody region 106.

A depth of the third body region 109 may be deeper than that of thefirst body region 106. That is, the lowest end of the third body region109 may be formed on a position deeper than that of the first bodyregion 106. The third body region 109 may be positioned between theadjacent gate electrodes 118. A maximum value of an electric field in apower semiconductor device may vary according to the width W of thethird body region 109, which will be described below.

Source regions 108 of a first conductive type may be formed below theupper surface of the drift region 104 and in the first body region 106.The source regions 108 have a concentration of the first conductive typehigher than that of the drift region 104. Depths of the source regions108 are shallower than that of the second body region 107. That is, thelowest end of the second body region 107 is formed on a position deeperthan those of the source regions 108. The source regions 108 may beformed on a position that overlaps a portion of the gate electrode 118and a portion of the source electrode 120.

A gate insulating layer 116 may be formed on channel regions 114 of thefirst body regions 106 and on the drift region 104 between the firstbody regions 106. The gate electrode 118 is formed on the gateinsulating layer 116.

The source electrode 120 electrically connected to the source region 108and a drain electrode 122 electrically connected to the drain region 102are respectively formed. The source electrode 120 and the drainelectrode 122 respectively are disposed on the surfaces, facing eachother, of the drift region 104.

A highly doped drift region 112 of a first conductive type may be formedbelow the upper surface of the drift region 104 between the first bodyregions 106, that is, may be formed in the drift region 104 below thegate electrodes 118. The highly doped drift region 112 is doped with thesame first conductive type as the drift region 104, and may be dopedhigher than the drift region 104. The highly doped drift region 112 mayhave a depth shallower than that of the first body region 106. Also, thehighly doped drift region 112 may have a depth deeper than that of thesource region 108. The highly doped drift region 112 is formed to reducea JFET resistance-component of resistance components that constitute anon-resistance.

A width a of the drift region 104 that overlaps the gate electrode 118between the first body regions 106 may be a width by which a depletionregion formed by extending from the first body region 106 may form aplanar junction structure.

In order to prevent the phenomenon of reducing a breakdown voltage byconcentrating electric fields on an edge of the first body region 106,the smaller the width a between the first body regions 106 is better.However, if the width a of the drift region 104 that overlaps the gateelectrode 118 between the first body regions 106 is small, a JFET regionmay be reduced, and, as a result, a rapid increase in a JFET resistancemay occur. The highly doped drift region 112 may mitigate the problem ofrapid increase of JFET resistance to some degree but, there is a limitdue to the shallow depth of the highly doped drift region 112.

In the current inventive concept, due to the third body region 109protruding from the lower end of the first body region 106, the increasein a JFET resistance and simultaneously a phenomenon of concentrating anelectric field on the edge of the first body region 106 may be preventedwithout reducing the width a of the drift region 104.

FIG. 2 is a cross-sectional view showing a doping profile of the powersemiconductor device of FIG. 1, according to an embodiment of theinventive concept.

In FIGS. 1 and 2, like reference numerals indicate substantially likeelements, and thus, the descriptions of elements described in FIG. 1 arenot repeated.

A third doping profile 110 having a third doping concentration of asecond conductive type is formed in the drift region 104. A first dopingprofile that has a boundary coinciding with a boundary of the first bodyregion 106 and has a first doping concentration of a second conductivetype are formed in the drift region 104. A second doping profile thathas a boundary coinciding with a boundary of the second body region 107and has a second doping concentration of a second conductive type areformed in the drift region 104. Accordingly, the third body region 109may correspond to a region below the first body region 106 of the thirddoping profile 110.

The third doping concentration is lower than the first dopingconcentration of a second conductive type, and the second dopingconcentration is higher than the first doping concentration of a secondconductive type.

FIG. 3 is a layout of a portion of a power semiconductor deviceaccording to another embodiment of the inventive concept. FIG. 4 is alayout showing a frame region and a body region of a power semiconductordevice according to another embodiment of the inventive concept. Across-sectional view taken along line A-A′ of FIG. 3 may correspond tothe cross-sectional view of FIG. 1. In FIGS. 1, 3 and 4, like referencenumerals indicate like elements, and thus, descriptions thereof will notbe repeated.

An entire cell is surrounded by an outermost frame region 200, and anupper part and a lower part of the outermost frame region 200 aremutually connected in a vertical direction by the first body region 106.That is, the upper part of the first body region 106 is connected to theupper part of the outermost frame region 200, and the lower part of thefirst body region 106 is connected to the lower part of the outermostframe region 200. The width a between the adjacent first body regions106 may be formed small enough to have a small value. Edges 200 c of theoutermost frame region 200 may be formed to have a radius of curvaturegreater than a predetermined size, for example, greater than 100 μm toprevent the formation of a spherical junction structure. Also, edges ofthe first body region 106 may have a radius of curvature greater than100 μm.

The first body region 106, the gate insulating layer 116, and the gateelectrode 118 may be disposed in a stripe type. Left and right sides ofthe gate electrode 118 are surrounded by the first body regions 106, andupper and lower sides of the gate electrode 118 and a side surface ofthe outermost gate electrode 118 contact the frame region 200. Thesource electrode 120 is disposed in a stripe type between the adjacentgate electrodes 118 by separating a predetermined distance from the gateelectrodes 118. The source region 108 is formed long along a sidesurface of the gate electrode 118, and additional source regions 108 afor connecting the adjacent source regions 108 to each other are formedto be connected to the source electrode 120 across the first body region106.

FIG. 5 is a layout of a power semiconductor device according to anotherembodiment of the inventive concept. A cross-sectional view taken alonga line B-B′ of FIG. 5 may correspond to the cross-sectional view ofFIG. 1. In FIGS. 1 and 5, like reference numerals indicate likeelements, and thus, the descriptions thereof will not be repeated.

Referring to FIG. 5, a power semiconductor device having a polygonalstructure unit cell is depicted. In order for the power semiconductordevice, for example, a MOSFET to have a high breakdown voltage and a lowon-resistance characteristic, hexagonal shape unit cells are disposed inequal distances d. Because the power semiconductor device is formed in apolygonal structure, a channel density per unit area may be increased.Accordingly, the effect of reducing on-resistance may be achieved.

FIG. 6 is a cross-sectional view of a power semiconductor device, forexample, a MOSFET, according to another embodiment of the inventiveconcept. In FIGS. 1, 2 and 6, like reference numerals indicate likeelements, and thus, the descriptions thereof will not be repeated.

Referring to FIG. 6, unlike in FIG. 1, the highly doped drift region 112may be formed not only between the first body regions 106 but alsodeeper than the source region 108, the first body region 106, the secondbody region 107, and the third body region 109. The highly doped driftregion 112 may have the same conductive type as the drift region 104,and may be doped to a concentration higher than that of the drift region104. The highly doped drift region 112 is a region for reducing a JFETresistance component of resistance components that constitute anon-resistance.

In FIG. 1, the highly doped drift region 112 is introduced to mitigate arapid increase of the JFET resistance due to the reduction of the JFETregion. However, a sufficient effect may not be expected due to shallowdepth of the highly doped drift region 112. However, as shown in FIG. 6,when the highly doped drift region 112 is formed deeper than the sourceregion 108, the first body region 106, the second body region 107, andthe third body region 109, the problem of rapidly increasing of the JFETresistance may be effectively prevented.

FIG. 7 is a cross-sectional view of a power semiconductor device, forexample, a MOSFET, according to another embodiment of the inventiveconcept. In FIGS. 1, 2, and 7, like reference numerals indicate likeelements, and thus, the descriptions thereof will not be repeated.

Referring to FIG. 7, the highly doped drift region 112 depicted in FIG.1 is not included in the semiconductor device in FIG. 7. Accordingly,the small width a of the drift region 104 that overlaps the gateelectrode 118 between the first body regions 106 may be a burden to theoperation of the semiconductor because the JFET resistance may berapidly increased.

However, the increase in the JFET resistance and the concentration of anelectric field on the edge of the first body region 106 may besimultaneously prevented due to the third body region 109 formed byprotruding on the lower end of the first body region 106.

FIG. 8 is a cross-sectional view of a power semiconductor device, forexample, an insulation gate bi-polar transistor (IGBT), according toanother embodiment of the inventive concept.

Referring to FIG. 8, a drift region 804 of a first conductive type maybe formed on a collector region 802 of a second conductive type, whereinthe collector region 802 may be a semiconductor substrate. Aconcentration of impurities in the drift region 804 may be reduced fromtop to down. The drift region 804 may have a concentration of the firstconductive type lower than that of the collector region 802.

A first base region 806 of a second conductive type may be formed on anupper predetermined region of the drift region 804. That is, the firstbase region 806 is formed below a upper surface of the drift region 804.The first base region 806 may be formed in a region where the driftregion 804 overlaps with a portion of gate electrodes 818 and an emitterelectrode 820.

A second base region 807 of a second conductive type may be formed belowthe upper surface of the drift region 804 and in the first base region806. The first base region 806 may have a doping concentration lowerthan that of the second base region 807. The second base region 807 hasa depth shallower than that of the first base region 806. That is, thelowest end of the first base region 806 is deeper than that of thesecond base region 807. In the current inventive concept, “is formeddeeper” denotes that a distance from the upper surface of the driftregion 804, on which the gate electrodes 818 are formed, towards thecollector region 802 is farther in a vertically downwards direction.

A third base region 809 of a second conductive type may be formed byprotruding downwards from a lower end of the first base region 806. Thethird base region 809 may have a concentration of the second conductivetype lower than that of the first base region 806. Also, the third baseregion 809 may have a concentration of the second conductive type lowerthan that of the second base region 807. The third base region 809 has adepth deeper than that of the first base region 806. That is, the lowestend of the third base region 809 is deeper than that of the first baseregion 806. The third base region 809 may be positioned between the gateelectrodes 818 adjacent to each other. A maximum value of an electricfield in the power semiconductor device may vary according to a width wof the third base region 809.

An emitter region 808 of a first conductive type may be formed below anupper surface of the drift region 804 and in the first base region 806.The emitter region 808 has a concentration of the first conductive typehigher than that of the drift region 804. The emitter region 808 has adepth shallower than that of the second base region 807. That is, thelowest end of the second base region 807 is deeper than that of theemitter region 808. The emitter region 808 may be formed on a positionwhere it overlaps with a portion of the gate electrode 818 and a portionof an emitter electrode 820.

A gate insulating layer 816 may be formed on channel regions 814 of thefirst base region 806 and on the drift region 804 between the first baseregions 806. A gate electrode 818 may be formed on the gate insulatinglayer 816.

The emitter electrode 820 electrically connected to the emitter region808 and a collector electrode 822 electrically connected to thecollector region 802 are respectively formed. The emitter electrode 820and the collector electrode 822 are respectively formed on surfaces,facing each other, of the drift region 804.

In order to prevent the reduction of a breakdown voltage of the powersemiconductor device due to the concentration of an electric field onedges of the first base region 806, the smaller width a between thefirst base regions 806 is the better. However, when the width a of thedrift region 804 that overlaps the gate electrode 818 between the firstbase regions 806 is small, a problem of rapidly increasing anon-resistance may occur.

In the current inventive concept, due to the third base region 809 thathas a doping concentration lower than that of the first base region 806of a second conductive type and is formed by protruding from the lowerend of the first base region 806, the increase in a resistance and aphenomenon of concentrating an electric field on the edge of the firstbase region 806 may be simultaneously prevented without reducing thewidth a of the drift region 804.

FIG. 9 shows simulation results of doping concentrations with respect toa power semiconductor device according to an embodiment of the inventiveconcept.

Referring to FIG. 9, test results are shown in images (a) through (d).First, FIG. 9 (a) is the simulation result of doping concentration of apower semiconductor device A that does not have the third body region109 (refer to FIG. 1). FIG. 9 (b) is the simulation result of dopingconcentration of a power semiconductor device B that has the third bodyregion 109 (refer to FIG. 1) having a width w (refer to FIG. 1) of 2 μm.FIG. 9 (c) is the simulation result of doping concentration of a powersemiconductor device C that has the third body region 109 (refer toFIG. 1) having a width w (refer to FIG. 1) of 3 μm. FIG. 9 (d) is thesimulation result of doping concentration of a power semiconductordevice D that has the third body region 109 (refer to FIG. 1) having awidth w (refer to FIG. 1) of 4 μm.

Referring to FIG. 9 (b) through (d), it is seen that the dopingconcentration of the second conductive type is gradually reduced fromthe second body region 107 (refer to FIG. 1) towards the third bodyregion 109 (refer to FIG. 1) through the first body region 106 (refer toFIG. 1).

FIG. 10 shows simulation results of field effects generated in a powersemiconductor device according to an embodiment of the inventiveconcept. FIG. 10 (a) through (d) respectively correspond to the cases ofFIG. 9 (a) through (d). A line A-A′ in FIG. 10 is a positioncorresponding to the depth of 2 μm from the upper surface of the driftregion 104 (refer to FIG. 1).

Referring to FIG. 10, in the power semiconductor device A that does nothave the third body region 109 (refer to FIG. 1), it is confirmed thatan electric field E is concentrated on an edge region of the first bodyregion 106 (refer to FIG. 1). The concentration of an electric field Emay cause a phenomenon of reducing a breakdown voltage.

However, in the power semiconductor devices that have the third bodyregion 109, it is confirmed that the phenomenon of concentrating anelectric field E on an edge of the first body region 106 (refer toFIG. 1) is mitigated. Accordingly, the presence of the third body region109 (refer to FIG. 1) may prevent the reduction of a breakdown voltagein the power semiconductor device.

FIG. 11 is a graph showing the magnitude of an electric field along theline A-A′ of FIG. 10. Lines (a) through (d) in FIG. 11 respectivelycorrespond to FIG. 9 (a) through (d) and FIG. 10 (a) through (d).

Referring to FIG. 11, it is confirmed that the electric field graduallyincreases along the line A-A′ of FIG. 10, and after showing a maximumvalue at a P-N junction region (for example, at the edge of the firstbody region 106 of FIG. 1), it gradually decreases.

In the power semiconductor devices B, C, and D that respectively havethe third body regions 109 (refer to FIG. 1), the magnitude of theelectric field at the edge of the first body region 106 (refer toFIG. 1) is smaller than that in the power semiconductor device A thatdoes not have the third body regions 109 (refer to FIG. 1). Also, in thepower semiconductor device C that has the third body regions 109 havinga width w (refer to FIG. 1) of 3 μm, the magnitude of the electric fieldat the edge of the first body region 106 (refer to FIG. 1) is smallerthan that in the power semiconductor device B that has the third bodyregions 109 (refer to FIG. 1) having a width w of 2 μm. Also, in thepower semiconductor device D that has the third body regions 109 havinga width w (refer to FIG. 1) of 4 μm, the magnitude of the electric fieldat the edge of the first body region 106 (refer to FIG. 1) is smallerthan that in the power semiconductor device C that has the third bodyregions 109 (refer to FIG. 1) having a width w of 3 μm.

That is, it is confirmed that, as the width w of the third body regions109 (refer to FIG. 1) increases, the magnitude of the electric field atthe edge of the first body region 106 (refer to FIG. 1) is greatlyreduced.

FIG. 12 is a graph showing a test result of a relationship between abreakdown voltage and a specific resistance R_(sp) in a powersemiconductor device according to an embodiment of the inventiveconcept. Cases A through D respectively correspond to the FIG. 9 (a)through (d), FIG. 10 (a) through (d), and the lines (a) through (d) inFIG. 11. The value of specific resistance R_(sp) represents anon-resistance per unit area of a power semiconductor device.

Referring to FIG. 12, it is seen that the power semiconductor device Bthat has the third body region 109 (refer to FIG. 1) having a width w of2 μm has a specific resistance R_(sp) lower than that of the powersemiconductor device A that does not have the third body region 109(refer to FIG. 1). Also, it is seen that, as the width w of the thirdbody region 109 (refer to FIG. 1) increases, the increase in thespecific resistance R_(sp) is minimized, but the breakdown voltage isremarkably increased.

Accordingly, according to the technical spirit of the current inventiveconcept, a low on-resistance may be realized by using a further higherdoping concentration (a low specific resistance R_(sp)) and a furthersmaller thickness of a drift region, and thus, a power semiconductordevice having a high breakdown voltage may be realized.

FIGS. 13 through 16 are cross-sectional views for explaining a method offabricating a power semiconductor device according to an embodiment ofthe inventive concept. In FIGS. 1 and 2 and 13 through 16, likereference numerals indicate like elements, and thus, the descriptions ofelements that are described with reference to FIGS. 1 and 2 will not berepeated. Operations for forming the source electrode 120, the gateinsulating layer 116, and the gate electrode 118 are well known in theart, and thus, descriptions thereof will be omitted.

Referring to FIG. 13, an operation for forming a drain region 102 of afirst conductive type and an operation for forming a drift region 104 ofa first conductive type on the drain region 102 are performed. Next, athird doping profile 110 having a third doping concentration of a secondconductive type is formed in the drift region 104 by an ionimplantation.

Referring to FIG. 14, a first doping profile having a first dopingconcentration and having a boundary coinciding with the boundary of thefirst body region 106 is formed in the drift region 104 by an ionimplantation.

Referring to FIG. 15, a fourth doping profile having a first dopingconcentration and having a boundary coinciding with the boundary of thesource region 108 is formed in the drift region 104 by an ionimplantation.

Referring to FIG. 16, a second doping profile having a second dopingconcentration and having a boundary coinciding with a boundary of thesecond body region 107 is formed in the drift region 104 by an ionimplantation.

In the method of fabricating a power semiconductor device according toan embodiment of the inventive concept, the operations described inFIGS. 13 through 16 may be sequentially performed in the stated order.However, the method of fabricating a power semiconductor deviceaccording to the inventive concept is not limited to the order statedabove. In modified embodiments, the operations for forming the firstdoping profile, the second doping profile, and the third doping profilemay be performed in an arbitrary order.

While the inventive concept has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims.

What is claimed is:
 1. A method of fabricating a power semiconductordevice, the method comprising: forming a drain region of a firstconductive type; forming a drift region of a first conductive type onthe drain region; forming a first body region of a second conductivetype below an upper surface of the drift region; forming a second bodyregion of a second conductive type having a depth shallower than thedepth of the first body region below the upper surface of the driftregion and in the first body region; forming a third body region of asecond conductive type protruded downwards from a lower end of the firstbody region; forming a source region of a first conductive type having adepth shallower than the depth of the second body region below the uppersurface of the drift region and in the first body region; forming a gateinsulating layer on channel regions of the first body regions and on thedrift region between the first body regions; forming a gate electrode onthe gate insulating layer; forming a source electrode electricallyconnected to the source region; and forming a drain electrodeelectrically connected to the drain region.
 2. The method of claim 1,wherein the first body region has a doping concentration of the secondconductive type lower than that of the second body region, and the thirdbody region has a doping concentration of the second conductive typelower than that of the second body region.
 3. The method of claim 1,wherein the forming of the first body region is performed afterperforming the forming of the third body region and the forming of thesecond body region is performed after performing the forming of thefirst body region.